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Onan JB Thermomagnetic Choke


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  #41  
Old 08-19-2017, 09:35:41 AM
Max Thompson Max Thompson is offline
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Default Re: Ground lugs

Quote:
Originally Posted by Leon N. View Post
I hope someone on the Stak can provide the factory build sheet for your plant. I think all they need is what you stated earlier: Mod. 7.52B, serial 0173550945 JB 3CR 8389T.
I did not find his model in a spec. T, closest I could get is spec. S. I did find a JC sheet for the same model in a spec. T.

Maybe Mike or Kevin can do better.
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  #42  
Old 08-19-2017, 05:42:08 PM
Leon N. Leon N. is offline
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Default Re: Ground lugs

Max thank you for providing that information. Something does not exactly add up. That is JoeE indicated his model number is 7.5JB-3CR/8389T. I wonder if he is mistaken and it should be rev S? If that factory build sheet you show is his machine, then he has a tri-fueled carburetor which means the internal parts are tougher than the straight gas jobs. Also, the vacu flow cooling makes sense if intended for a mobile home but it was wired for 120 VAC only where as the build sheet shows 120/240. Could this JB have had two previous owners? We need answers from JoeE.

Also, the build sheet indicates the control wiring diagram is 611C804 which by the way can be found on page 82 in 967-500.
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  #43  
Old 08-19-2017, 10:57:41 PM
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Default Re: Ground lugs

I got that information off an envelope with some receipts that the previous owner had. That is the information he wrote down on it.
Next time I go up to where the machine is at, I'll take a pic of the data plate.

It is field reconnectable... single phase... in 2 and 3 wire configurations.... 120 and 240.
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  #44  
Old 08-20-2017, 07:50:38 PM
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Default Re: Onan JB Thermomagnetic Choke

Here is an up-close shot of the data plate..
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  #45  
Old 08-21-2017, 06:57:59 AM
Max Thompson Max Thompson is offline
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Default Re: Onan JB Thermomagnetic Choke

Sorry, still no luck finding the build sheet for spec. T. Some build sheets did not make it from the paper files to the data base we use.
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  #46  
Old 08-29-2017, 05:01:19 PM
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Default Getting ready to clean the thing up...

I was going to go pressure wash this thing to get the build-up grease and dirt off of it... So I thought I would take the rocker arm cover off the cylinders and look in there... I was pleasantly surprised to see it's nice and clean up top.
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  #47  
Old 08-29-2017, 05:02:37 PM
JoeE. JoeE. is offline
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Here's a photo...
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  #48  
Old 08-29-2017, 07:48:42 PM
Leon N. Leon N. is offline
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Default Re: Onan JB Thermomagnetic Choke

If we cannot find the factory build sheet, the next best thing can someone interpret or decode the optional,equipment as shown by the numbers 8389. That would describe the optional equipment which may be simply that the plant's output wires were arranged for 120'volts only. This can, I believe, easily be reconnected for 120/240 if needed.
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  #49  
Old 08-29-2017, 09:19:50 PM
MBB MBB is offline
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Default Re: Onan JB Thermomagnetic Choke

Here is the decode of the 8389. See 179
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  #50  
Old 08-30-2017, 01:25:07 AM
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Default Re: Onan JB Thermomagnetic Choke

If you have the valve covers off, it would be a good time to check the valve clearances, check that the oilier in the cover is clean and flows, check that the small feed lines that feed the rocker oiliers are clean and flow.
Your engine is an easy one to adjust the valves on. First un-clip the distributor cap and just pull it away from the distributor so you can see the rotor on the distributor shaft. Turn the engine by hand and "aim" the rotor to the same position that would line up with the plug wire position on the distributor cap when you place the cap back on to the distributor body. With the rotor pointed to one of the four plug wire positions on the distributor cap, follow that plug wire to the spark plug. That cylinder is ready to adjust the two valves, the intake and the exhaust. Repeat turning the engine 180 degrees the same direction to the next distributor wire location. Follow that wire and adjust the two valves. Repeat for the next two cylinders. This method works on any engine with a distributor. point the rotor to each plug wire location on the distributor cap, follow that wire and adjust that cylinder.
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  #51  
Old 08-30-2017, 01:56:27 AM
Ray Lynch Ray Lynch is offline
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Default Re: Onan JB Thermomagnetic Choke

Quote:
Originally Posted by Motorhead View Post
If you have the valve covers off, it would be a good time to check the valve clearances, check that the oilier in the cover is clean and flows, check that the small feed lines that feed the rocker oiliers are clean and flow.
Your engine is an easy one to adjust the valves on. First un-clip the distributor cap and just pull it away from the distributor so you can see the rotor on the distributor shaft. Turn the engine by hand and "aim" the rotor to the same position that would line up with the plug wire position on the distributor cap when you place the cap back on to the distributor body. With the rotor pointed to one of the four plug wire positions on the distributor cap, follow that plug wire to the spark plug. That cylinder is ready to adjust the two valves, the intake and the exhaust. Repeat turning the engine 180 degrees the same direction to the next distributor wire location. Follow that wire and adjust the two valves. Repeat for the next two cylinders. This method works on any engine with a distributor. point the rotor to each plug wire location on the distributor cap, follow that wire and adjust that cylinder.
Chris
Think your describing valve adjustment for a JC. He has got a JB. No distributor.
Ray
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  #52  
Old 09-02-2017, 12:51:25 PM
JoeE. JoeE. is offline
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Default Re: Onan JB Thermomagnetic Choke

Do you reckon that where these two bolts are located on the rocker cover is where a lifting point ought to be located?
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  #53  
Old 09-02-2017, 03:00:04 PM
Leon N. Leon N. is offline
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Default Re: Onan JB Thermomagnetic Choke

JoeE what are you doing as shown in your picture of the JB rocker cover??? Those two bolts you show do not look like the original ones? Certainly not the one to the left. There are four not too long , I believe 1/2 inch socket head x what one inch or so with bolt heads that should be torqued down to 8-10 ft lbs. See page 6 in 967-500.

The lifting bracket is attached to the rocker arm cover with one bolt which takes a 3/4 inch socket. You do not show the Onan designed lifting bracket? Unless you have a different design, I question what you are trying to do. See attached picture.

JoeE that picture in your post # 52 leads me to suspect someone is toying with the idea of improvising a mount to lift your JB by attaching a bracket to only two of the rocker cover bolts by substituting longer rocker cover hold down bolts. If you do that you will really damage your JB because two half inch bolts cannot support 475 + pounds.

The Onan lifting bracket is attached with one humongus bolt to the rocker cover. The load is distributed equally between the 4 half inch rocker cover bolts. That's what about 475+/4 or 120 pound on each thread into aluminum casting. Please watch out or you will at least distort you cylinder head, etc. Just my two cents. See second photo.
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Last edited by Leon N.; 09-02-2017 at 03:36:49 PM. Reason: added info
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  #54  
Old 09-02-2017, 06:27:48 PM
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Default Re: Onan JB Thermomagnetic Choke

Yes, the one half inch bolt on the Rocker cover is what I was asking about... And the one 5/16 bolt over on the left... it seems to have an extension on it .....I thought maybe they were both used.. I had never seen a picture like you've shown of a bracket mounted on the engine... Seems odd to me that the one single bolt on the rocker cover can take 400 lb
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  #55  
Old 09-02-2017, 07:06:31 PM
Leon N. Leon N. is offline
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Default Re: Onan JB Thermomagnetic Choke

JoeE to answer your question in your post #52 and #54, the answer is definitely a NO NO! Like I said whom ever you got this JB from did not know what he was doing.

Yes it seems odd and I questioned this with the Onan Corp way back in 1970 when I refurbished my JB. ONan was emphatic that yes the lifting design will work as intended with a big caveat. That is no other accessories should be connected or lifted with the arrangement shown in my post. That means mufflers, skids, eye. I have personally lifted my JB several times as shown with know problems.

The basic JB weighs in at 475 pounds. Like I said, you can calulate from your strength of materials class, the stresses and you will quickly conclude there is a safety margin in the Onan lifting bracket assembly. Unknowingly, back many moons ago, I unwittingly lifted my Onan muffler and 4x4 mounting skids with no problem. But if you attempt to put all that weight on only two bolts, the bolts may not break but the threads may let go, I do not know, but why not follow the Onan information found in 967-320 & 967-500. Otherwise continue to use those straps as you have shown. Hate to see you have TR with such a gem.
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  #56  
Old 09-02-2017, 08:51:54 PM
len k len k is online now
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Default Re: Onan JB Thermomagnetic Choke

I don't think bolt would break long as there are no side loads, weak point should be ripping the threads out of aluminum cover. Aluminum is much weaker than steel and especially much weaker than the high strength steels of good bolts. Potential saving grace is I think cover is thick.

I gave it a very quick look in a spreadsheet I wrote for work and 5/16 unc bolt might take ~4000 pounds before Von Mesis stress at thread goes to ~ 100,000 psi. I suspect this is below strength of grade 8 bolts, I didn't look it up. UNF thread can take more , ~ 4100 pounds at less stress ~ 90,000 psi. Stress in "nut" thread is slightly less as it's thread "root" dia is slightly larger than bolt's But aluminum is MUCH weaker than these high strength steels, and I suspect it's close to yielding while lifting gen. So take it easy while lifting gen.

Yoda said Onan says gen only, no lifting skids, bats or fuel tanks also.
.

Last edited by len k; 09-03-2017 at 03:12:41 PM.
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  #57  
Old 09-03-2017, 10:55:43 AM
Max Thompson Max Thompson is offline
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Default Re: Onan JB Thermomagnetic Choke

Leon: Your lifting bracket may be an older style. They later went to a large(aprox. 6" square) lifting bracket that bolted in 2 places. The spacer on the valve cover bolt was located under the lifting bracket.

https://www.smokstak.com/forum/showthread.php?t=89113 In post 17 of the linked thread, 2nd picture. The set on the right side has the type bracket I am talking about. This was the handiest picture I could come up with.
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  #58  
Old 09-03-2017, 11:24:14 AM
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Default Re: Onan JB Thermomagnetic Choke

Looks like a couple of different lifting brackets . They only show one in the picture but in the description and part numbers they show one with a eyebolt.
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  #59  
Old 09-03-2017, 11:25:31 AM
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Default Re: Onan JB Thermomagnetic Choke

Forgot the picture.
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  #60  
Old 09-03-2017, 02:50:12 PM
Leon N. Leon N. is offline
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Default Re: Onan JB Thermomagnetic Choke

Max re your comment: "Your lifting bracket may be an older style." If you call my 1966 built JB the old style, so be it. All I am saying is that his comment about "two bolts" in post 52 does not compute to me. Two bolts, albeit the rocker cover bolts will not support the JB as the author seems to think. No way. There must be more to it.

Note the cover shown in post 52 does not look like the cover illustrated in post 59. Not sure where Kpack got his information and more importantly does it apply to the author's JB. Could Kpacks info apply to the YD models and NOT the magneciters? Something does not add up here? Could the YD models be lighter than the Magneciter models?

I do believe the magneciter back end is heavier than the front end JB engine.

Last edited by Leon N.; 09-03-2017 at 03:00:26 PM. Reason: more info
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